Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Transmission from a base-station to a mobile device may be spread across in time and frequency using a spreading technique, such as orthogonal frequency division multiple access (OFDMA). A spreading technique may be used in some mobile communication standards, such as Long Term Evolution (LTE), by assigning time and frequency slots to individual user devices.
Peak-to-average-power ratio (PAPR) is a concern that typically occurs in orthogonal frequency division multiplexing (OFDM) modulation. OFDM is used in multiple communication technologies such as WiFi, WiMAX, LTE-Advanced, and similar ones for applications such as digital television, wireless networks, and 4G mobile communications.
For an N-carrier OFDM signal, PAPR may equal about N, where N is an integer greater than or equal to 2. At certain time instances, individual contributions from the subcarriers may align in phase and large magnitudes may be observed in the baseband signal. These large amplitudes may force power amplifiers to either work in the non-linear regions giving rise to large signal distortion, or to work far from the amplifier saturation region, which may lead to power inefficiencies. High PAPR may also involve the use of high-precision digital-to-analog converters (DACs), thereby increasing cost of equipment.